Leak testing is known as a technology of examining airtightness of a test workpiece having an internal space. Particularly, in a case where the test workpiece is a micro-sized electronic component such as a quartz oscillator and an MEMS (Micro Electro Mechanical Systems), a dipping method (bombing method) is employed in order to enhance sensitivity (refer to JIS Z 2331 (2006), JIS C 60068-2-17, Patent Literature 1, and the like). As described in Patent Literature 1, in the dipping method, the test workpiece is put into a bombing tank, and is allowed to stand until a desirable bombing time elapses, in a state where the inside of the bombing tank is pressurized by helium gas (inspection gas). At this time, in a test workpiece having good airtightness, helium does not enter at all or scarcely enters the inside of the test workpiece. On the other hand, in a test workpiece having a defect in airtightness, helium enters the inside of the test workpiece through the defect part. When the bombing time elapses, the test workpiece is taken out from the bombing tank to be put into a vacuum chamber. Gas in this vacuum chamber is evacuated, and helium in this exhaust is detected. In a case where the airtightness of the test workpiece is good, a detected flow rate of helium is limited to a level equivalent to the background. On the other hand, in a case where the airtightness of the test workpiece is failure, helium that enters in bombing leaks, so that helium that largely exceeds the background is detected. Consequently, it is possible to determine the quality of the airtightness of the test workpiece.
Recently, in the micro-sized electronic component such as the quartz oscillator and the MEMS, the request level of the airtightness becomes more severe, and further improvement of detection sensitivity for leaked helium is requested. As one of the methods, a so-called accumulation method is proposed (e.g., Patent Literature 2). In the accumulation method, leaked helium from a test workpiece is accumulated in a chamber for a predetermined accumulation time, and helium partial pressure is increased, and thereafter detection is performed. Therefore, it is possible to reliably perform detection even when the leak is minute.